In part 1, I went over what the core is and the function of core stiffness in relation to sporting performance and optimal force and power output. To recap: core stiffness may refer to the core's ability to maintain stability in response to the influence of external forces, which may vary in magnitude, direction and speed.

Highly recommend reading part 1 before continuing on with this article.

In part 1, I mentioned that improving performance via increased core stiffness will depend on multiple variables:

The nature of the sport and the energy systems involved (How long is the core braced for? Does the athlete need more strength? Or more endurance?)

The properties of the movement itself and the speed of core stiffening

The magnitude of core stiffening (stiffer doesn't always mean better, remember: fast and powerful athletes also need to learn how to relax at the right times - like the example of the punches and kicks we used earlier).

First off, I'd like to break this article up into 2 categories, short-term improvements in core stiffness and long-term improvements in core stiffness.

SHORT-TERM IMPROVEMENTS

Short-term improvements or increases in core stiffness, are characterized by improvements seen within the same training session. Known and performed as "core activation" drills among personal training circles, some claim that performing core exercises prior to the main exercises of a workout "wakes up" the core and improves performance on the subsequent exercises. While terms like "wake up" are very arbitrary, it helps to look a potential mechanism by which core activation drills help with short term performance.

Post Activation Potential

Benjamin Lee and Stuart McGill carried out a study in 2017 to measure the effects of short-term isometric training on core torso stiffness and found beneficial results. For the core isometric training protocol, participants performed the plank, side plank and bird dog exercises for 5 sets of 10 seconds - with coaching cues being offered and standardized to all participants. Using both passive and active torso bending trials, the results showed that most participants had reductions in torso deflection and increased core stiffness (more details here).

While this study showed that short-term core stiffness can be increased via isometric core exercises, it doesn't tell us how that core stiffness will transfer to performance in other exercises, or how long this effect lasts. In their discussion, the authors pointed to the fact that the isometric exercises done could have elicited a post activation potential (PAP).

PAP is a physiological/neurological phenomenon where strength and rate of force development (power) is increased due to previous near-maximal muscle contractions. The most common protocols may include heavy back squats to elicit a PAP effect before sprinting and jumping, or heavy presses before performing ballistic medicine ball pushes/throws. Utilizing the PAP effect is also known as complex training. Here are some examples of exercise pairings, from the NSCA.

Taken from https://www.nsca.com/Education/Articles/Hot-Topic-Post-Activation-Potentiation-%28PAP%29/

For a concise explanation of the potential mechanisms behind PAP and how it works, visit Science For Sport.

Back to the study. While the authors pointed out the PAP mechanism, they acknowledged that their core training protocol, despite improving core stiffness, did not meet the requirements of a "potentiating exercise". In a standard PAP protocol, the potentiating exercise has to be close to max effort, with the recovery time reflecting the nature of exercise. Lee & McGill's (2017) study's core training protocol included 5 sets of non-fatiguing core exercises (only 10 seconds long - bodyweight, no added resistance), so I'd be interested to see if there could be a larger PAP effect if some core exercises are taken to near max effort. Here are some ideas:

Planks are one of the most frequently prescribed core exercises in the fitness and strength training. An easy way to increase the difficulty of the plank is to add extra resistance - perform them weighted. In this complex set, the weighted planks act as the potentiating exercise, increasing the the power output of the slams. While the effort should still be high during the planks, the physiological stress is relatively low compared to for example, a set of heavy front squats; meaning the recovery time should be lower than most heavy compound movements. A recovery time of 2 minutes should be adequate before performing the medicine ball slams.

In this example, I use an anti-rotation exercise to potentiate a ballistic exercise for better power transfer. I also added a small rotation component to what would normally be an anti-rotation exercise (the pallof press) to mimic some of the movements seen in the medicine ball rotation throw. Keep in mind, I still maintain tension on my obliques working and the shoulder girdle stable during the press out and rotation. Recovery time can be anywhere from 1 to 2 minutes.

Other Potential Ideas

Core Stiffness For Powerlifting

Aside from using higher effort complex sets, I have found situations where non-fatiguing core exercises can help improve the quality of a training session. For the last couple of months, I've been using bodyweight planks and shorter weighted plank sets with my powerlifters prior to the main compound lifts . Planks are a good way to emphasize whole body tension (a skill that is required for powerlifting success), to improve the lifters' perception on how active their core for the rest of the training session, and to remind them about the importance of a rigid torso during the powerlifts. Most, if not all of my powerlifters, have found this pre-lifting core work beneficial.

With this protocol, perform several sets of planks at a low RPE (non-fatiguing) to avoid overly fatiguing the core musculature before the compound lifts. More advanced trainees can experiment with planks at higher intensities to elicit a greater PAP response. Slowly increase the intensity of these planks over time to find the sweet spot (balance of volume and intensity).

Core Stiffness For Weightlifting

Another idea I've implemented in the past is the use of higher velocity core stiffening drills to help facilitate weightlifting technique improvements. The catch position of snatches and cleans require a lifter to quickly decelerate the weight by using the prime movers and stiffening the core upon bar contact. I've found depth drop landings or plyometric regression exercises to help with this. Here's a quick example with one of my Strongman/Powerlifting athletes, who was brand new to the Olympic lifts at the time. Used in conjunction with other coaching techniques, he made some good improvements just over the span of 3 months.

Intra-abdominal Pressure (IAP)

If you've spent anytime studying strength training or have spent time in the weight room, you probably heard of the concept of intra-abdominal pressure (IAP). Also referred to as "bracing", intra-abdominal pressure is a technique by which a trainee creates 360 degree pressure in the abdominal cavity through controlled inhalation. The created pressure helps stabilize the lumbar spine, reduce the risk of back injuries as well as improve force output. The concepts of core stiffening and creating intra-abdominal pressure are complimentary and much like the core stiffening concepts discussed previously, IAP is not an all or nothing phenomenon.

IAP happens on a continuum, and can vary in intensity and duration depending on the movement requirements of the task. Coaches around the world all stress the idea of creating IAP during strength training, however, not many of them can explain it as well as Chris Duffin (Kabuki Strength) and Stuart McGill. Kabuki Strength describes IAP as a continuum of respiration (breathing) and stabilization (max effort IAP), best represented by a dial.

To give an example, the lumbar stability needs during a 1RM compound lift is different than a sub-maximal activity like running. Running requires just enough IAP to stabilize the torso, while still allowing for optimal breathing. Turn the knob accordingly.

“Improving your ability to select and coordinate the correct dial setting is the key for fluid movement and higher performance in any activity”

— Kabuki Strength

long-term improvements

Long-term improvements in core stiffness are characterized by improvements seen over weeks and months of core training. This section will cover the different categories of core training, as well as general training principles that drive long term improvements.

Core Training Categorization

To start, it's best to differentiate between core exercises in order to better analyze their cost-to-benefit ratio. All exercises fall on a general to specific continuum, with the reference points being the movement you want to improve, or the sport/position you're playing - core exercises are no different. Dedicated core exercises can be broken down into several categories:

1. Isometric Core Exercises

Isometric exercises are exercises where force is produced without a change in muscle length. Exercises like planks and hanging L-Sit where you're maintaining your body position are examples of isometric core exercises.

2. Anti-Rotational Core Exercises

Anti-Rotational exercises also fall the "isometric" category. These exercises challenge your ability to stabilize your body to prevent from rotating to any one side, maintaining your body position against an external force or in an imbalanced position. Common exercises include the pallof press, shoulder taps in push up position and many exercises in the half kneeling position. Other great examples not many people know about could be suitcase deadlifts, and uneven farmers walks (videos below).

3. Isotonic Core Exercises (Sagital Plane/Transvere Plane)

Isotonic exercises are exercises that consist of an eccentric and concentric portion - exercises that are not isometric (holds). They can be further broken down into sagital/transverse plane exercises. Sagital plane exercises include standing cable crunches, sit ups and hanging leg raises, while transverse plane exercises involves any exercise that involve torso rotation like cable wood-choppers and medicine ball russian twists.

4. Ballistic and Plyometric Core Exercises

Ballistic exercises are concentric-dominant power movements with little to no eccentric muscle action, such as jump squats and explosive push ups. In the realm of core exercises, medicine ball slams, rotational throws can be considered ballistic, but keep in mind the prime movers such as the shoulders and glutes also contribute to the force output.

Plyometric exercises are exercises with a short eccentric-concentric turnover, using the elastic properties of our muscles to improve speed and repeated power output. Many movements like running, repeated jumps/hops and combination striking (in martial arts) are considered plyometric. There are also plyometric exercises designed just to target the core musculature - many of these being rotational. I've posted a few examples below:

Taken from Nick Curson (Speed of Sport)

Taken from Elliot Hulse

Training principles and methods To Improve Performance

Conversations usually go south whenever the topic of "transfer to performance" is brought up; there are many complex variables to take into consideration and everyone seems to have their own definition of "functional" or what exercises will and will not help improve performance. I'll be giving some general tips and training principles of core training that can be applied to various different sports.

Post-activation-potentiation, non-fatiguing core primers and intra-abdominal pressure are all acute techniques that CAN lead to long-term improvementsThe research is still not conclusive on whether these are significantly beneficial, but in theory: accumulating small short-term improvements should lead to long term improvements in performance. In other words, if these techniques are performed consistently throughout your training program, they may add up to a measurable increase in strength, power and endurance (whatever you're aiming for). I would also add that the use of PAP and core primers are optional, but in my opinion, IAP is not. I consider IAP a skill that must be learned and utilized consistently in order to effectively produce force, and stay safe doing so.

A combination of general and specific core exercises should be performedDon't fall into the "functional" trap of prescribing overly-specific exercises. A general exercise that does not fully mimic the movement you're trying to improve can still be beneficial. For example, weighted planks are a great general core exercise to build core strength and endurance that will transfer over to various movements. Once a good base is built, you can start experimenting with more specific exercises. I've included some examples of specific exercises at the end of this article, mainly geared towards improving punch power, but can also be used as core training.

Principle of progressive overloadThis is the premise behind improving any type of performance measure. Progressive overloading your core exercises either through a change in position, adding extra resistance, increasing the volume via sets, reps or time. In order to improve, you must progressively add stress to your physiological system, recover from it, and come back stronger.

Improving Core Strength (Slow-Isometric Stiffness)Core strength, or slower-isometric type core stiffness, is primarily built using isometric and anti-rotation based exercises. Almost every core exercise listed above can be used to improve core strength, but what differentiates training core strength from core endurance is the intensity at which these exercises are performed. Reps should be done in the lower rep range (~<6 reps per set) or 80-95% of 1RM if a 1RM is applicable. Accordingly, intensity/weight progression is what you should be focused on. For example, progressively working towards heavier weighted planks (increasing intensity) instead of increasing the time of which you hold body-weight planks. Improving core strength will benefit every athlete, but strength and power athletes will see the best results.

Improving Core Ballistic/Plyometric/Power Ability (Fast-Recruiment Stiffness)Core plyometric ability, or what I like to describe as a faster-recruitment type core stiffness, is built through plyometric core exercises and have a higher skill/timing component to it. This is the type of core stiffness I discussed in part 1, that is required for high-impact athletes who perform punching, kicking and striking movements. The ability to contract-relax-contract and produce a fast eccentric-concentric turnover is what defines an athlete with good core power and plyometric ability - both deceleration and acceleration are taken into account.

I gave examples of relatively advanced plyometric core training above (see Nick Curson and Elliot Hulse's videos). A more beginner friendly way to perform these exercises would be to reduce the range of motion on the exercises and reduce the power output until you improve your timing. A drill I found useful are short plyometric medicine ball rotation slams - timing and rhythm are paramount here so develop them before moving onto higher-intensity, higher-effort plyometrics.

Improving Core EnduranceWhen people think of the word "endurance" they immediately associate that with a low-intensity, long duration training protocol. Don't make the same mistake. Endurance can refer to the ability to maintain a certain power output for an extended period of time OR be able to repeatedly perform high-intensity bouts with little to no drop off in power output from start to finish. I recommend using work-to-rest ratios with your core exercises based on the energy system you want to develop.

Do you want to be able to repeat maximal high-intensity efforts? Use work rest ratios anywhere from 1:20 to 1:30+. For example, 6 seconds of maximum effort tornado ball slams with 2 minutes of complete rest in between sets, for several sets (1:20 work-rest ratio).

Looking for longer duration core endurance? Perform lower intensity core exercises for a total of 3 minutes+ at a time with a work-rest ratio of ~2:1. For example, hold a bodyweight plank for sets of 3 minutes with 1.5 minute rests in between. To add some variation to these longer sets, you can also perform 3-4 different core exercises as a circuit for 1 minute each. Over time, increase the duration of each set or the total number of sets (volume load progression at a set intensity).

Using work-to-rest ratios is another tool by which you can use to look at and utilize core training with. It can help you visualize which energy systems are at play, so you can make the adaptations you want to see. Endurance is specific.

Diminishing ReturnsMore core work means better performance right? Not so fast. Welcome to the principle of diminishing returns. The more you train core stiffness, the less benefits you reap in. I see core stiffness training a lot like maximal strength for sports. There comes a point where more core training does not equate to better performance on the field, court, platform or ring. Core stiffness, much like strength, serves as a foundation on which other important physical attributes are built on - rate of force development, agility, resilience to injury to name a few. Be careful not to allocate all of your time and energy into core stiffness training, while neglecting the development of other skills and attributes.

So how much is enough?

Unfortunately, I don't have a concrete answer for you. This really depends on what sport and movement patterns you're referring to. Core training should fill the gaps of your physical development, and be used in conjunction with sport-specific skill work and strength/power/plyometric training. Being able to competently perform all the movement patterns and core exercise categories listed above is a great start.

Biggest takeaway

If there's one thing you take away from this article, it's that core stiffness training is context-specificand should be thoughtfully prescribed and developed. Core training does not have to be boring, so don't be afraid to get creative. Below is some of my content I've put out on core training, core ballistic training and various medicine ball slam exercises. Thanks for reading!